NOISE & HEARING (KAS 3501) Year 3 (II) 2014/2015

Group 18May 13th 2015

MUHAMMAD NUH B SULAIMAN U K 3 0 0 0 6

WAN HAFIZAH BT WAN ZAKARIA U K 3 0 0 5 8

LEE SOOK YEEN U K 2 9 5 6 3

NABILA BT MD HANIF U K 3 0 1 0 4

NUR FARHANA BT MAT NOH U K 2 9 5 6 1

1. INTRODUCTION Noise is unwanted or offensive sounds that

unreasonably intrudes into our daily activities. Classified as physical hazard. May lead to permanent and irreversible damage to

hearing.

REGULATIONSo Factories and Machinery (Noise Exposure)

Regulation1989o Aim at protecting employees while they workso Regulation 5 – Permissible Exposures Limit

o No employee shall be exposed to noise level exceed continuous sound level of 90dB (A)

o No employee shall be exposed to noise level exceed 115dB (A) at any time

o No employee shall be exposed to impulsive noise exceed a peak sound level of 140dB (A)

NOISE CONTROL - CONCEPT AND BASIC PRINCIPLE

As in all hazard control, noise control efforts should be approached according to the hierarchy of control strategies, i.e. using the paradigm:

Noise from most equipment comprises mainly waste energy.

The best way to reduce noise is to tackle the problem at the source.

At the other end, reduction at receiver (i.e. affected employee) is achieved by either removing the employee from the sound field, limiting his working time in the area.

4. OVERALL NOISE CONTROL PROCEDURE

o Appropriate control measures includes;o Change in plant design and layouto Substitution of a less hazardous work methodo Reduction of the hazard at its sourceo Reduction of the hazard at its path of transmission.

Thus the recommended method of approach is outlined below; Plant planning (design and layout) Substitution (equipment, process, material) Engineering control Control at source (modification of noise generator) Control at path (modification of sound wave)

CONTROL BY PLANT PLANNING

Successful planning for noise control involves: Knowledge of the noise characteristics of each machine

and process; Proposed location of each noise source, operator, and

maintenance man; Selection of design criteria based on employee exposure

time.

It is important to consider the following: The building's load-bearing structure Powerful noise sources should be enclosed by structures Rooms where there are sound sources and where

personnel are present continuously should be provided with ceiling

Office areas should be separated from building elements where vibrating equipment is installed by a joint of elastic material.

CONTROL BY SUBSTITUTIONa) Use Quieter Equipment

The first step in providing quiet workplace equipment is to make a strong effort to have equipment purchase specifications include noise emission limits. When acquiring new equipment, its type and speed should be selected on the basis of the applicable noise criteria.

b) Use Quieter Processes In many cases, changing the process can be one way of getting to

grips with noise generation. This would in turn involve cooperation between the employer, supplier, process designer and OSH professional.

In most building and construction work, Hazardous local noise levels are generated both by the impact on the pile and from the explosion, and annoyance may be caused at distances of up to a few miles.

c) Use Quieter Material Materials from which buildings, machinery, piping and containers are

constructed have a vital relation to noise control. Some materials have high internal damping and are called 'dead' materials, while others called 'live' materials have little internal damping and cause a ringing sound when struck.

ENGINEERING NOISE CONTROL

Existing Equipment

a) Once generated, noise can transmit through;

i. Direct sound field

ii. Reverberant sound field

iii. Structure-borne path

b) Reduce amount of work hour in the sound field.

c) Proper maintenance of equipment.

ENGINEERING NOISE CONTROL

Systematic Approach

o Control noise from existing equipment by applying

engineering principal.

Generated noise

Radiated noise

Control at

source

Directly transmitted noise

Reverberant noise

Structure-borne noise

Control at

path

Control at receiver

Generated Noise

• Reduction or elimination of the impact and generation of noise• Modification of equipment which reduce the metal-to-metal contact

(eg: blade,gear etc)

Radiated Noise

• Move the machine to new place far from the exposed employees• Apply vibration isolation to machine housing

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Directly Transmitted Noise

• Use sound absorptive material• Construct and acoustical barrier to shield, deflect or absorb noise

energy

Reverberant Noise

• Use sound absorptive material (eg: fiberglass, acoustic tiles on wall, ceiling etc)

• Reduce reflection by move the machine far from corner or walls

Structure-borne Noise

• Use duct lines with sound-absorptive material• Use wrapping on pipe to increase their sound insulation

Use enclosure or control room to house the

employee.

Reduce the amount of time the employee is

allowed to work in a high noise area.

Provide HPE to the employee.CO

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REDUCING GENERATED NOISE

• Reduce Impact Noise• Reduce or Eliminate

Aerodynamically Generated Noise

• Reduce Vibration

REDUCE IMPACT NOISE

Mechanical and material handling devices- produce noise from impact

Reducing the dropping height of goods collected in boxes or bins

Using soft rubber or plastic to receive and absorb hard impacts

Increasing the rigidity of containers receiving impact goods and adding damping material — especially to large surfaces.

Regulating the speed or cycle time of conveyors to prevent collisions and excessive noise.

REDUCE OR ELIMINATE AERODYNAMICALLY GENERATED NOISE

• Change the character of the noise• Reduce the surface area of the source• Change the source dimensions such that

noise is cancelled out at the edges• Reduce or remove interrupted-wind tonal

noise• Reduce turbulence in fluids• Reduce fan noise• Use silencers• Reduce Vibration

CHANGE THE CHARACTER OF THE NOISE

Replacing a noise source with one of higher noise frequency may reduce the sound level at typical property-line distances

REDUCE THE SURFACE AREA OF THE SOURCE When large surfaces vibrate they will

produce high sound levels. Consider replacing solid plates, wherever possible, with expanded metal, wire mesh or Perforated

CHANGE THE SOURCE DIMENSIONS SUCH THAT NOISE IS CANCELLED OUT ATTHE EDGES

At the edges of large vibrating plates, the compression and rarefaction sound waves tend to cancel each other out using long narrow surfaces instead of square or approximately square surfaces

REDUCE OR REMOVE INTERRUPTED-WIND TONAL NOISE

When tonal noise is produced by machinery due to this effect, it maybe possible to eliminate the wind (i.e. the air flow) by filling out any hollow space, thus removing the noise created by it.

REDUCE TURBULENCE IN FLUIDS• Fluid noise is due to turbulence. The more turbulent

the flow, the greater would be the noise.• Vapour bubbles can be created by abrupt changes

in the flow of fluids. Providing gradual transition in cross-sectional area reduces the

likelihood of these bubbles forming

Turbulence at the walls of ducts or pipes is always present. To reduce noise;

Interior walls should be smooth, free of protrusions at joints, and sharp bends at 'tees' (T junctions) and 'wyes' (Y junctions) should be avoided.

Turning vanes can be placed inside ductwork when construction methods utilise sharp bends.

Straightening vanes can be used to smoothen the flow downstream of any change in direction, diameter, or branching

USE SILENCERSAbsorptive silencer: Simplest form: lined duct considered for cooling and exhaust air

whenever sources are to be enclosed

Reactive silencer: simplest form: single expansion chamber the expansion and contraction in pressure

cause reflection of sound waves. The reflected wave added to the incoming

sound wave results in destructive interference, leading to noise reduction.

REDUCE VIBRATION• Shifting instrument panel to wall• Putting damping on flexible panel• Obtaining maximum isolation by stiffening the floor

structure; or mounting the machine on ground-founded pillars

• Placing heavy vibrating equipment on inertial block with vibration isolators and dampers.

• Flexible connectors for preventing vibration transmission to building structure.

• Isolation of pipe work on refrigeration plant by use of flexible couplings

• Shifting small service machinery onto isolators on a solid floor

• Reducing resonance in a circular saw blade

CONTROLLING NOISE IN ROOMS

DEFINING SOUND FIELDS

Near Field The region close to a sound source usually defined as 1/4 of the longest wavelength of the source.Near field references can pertain to both indoor and outdoor environments.

Far Field Sound field beyond the near field limits described above where the sound pressure level (SPL) drops off at the theoretical rated of 6 dB for every doubling of distance from the source.

Direct Field To describe far field conditions that follow the Inverse Square Law SPL loss rate of 6 dB for every doubling of the distance. 

Diffuse Field There are so many reflections contributing to the total sound field that sound levels measured virtually anywhere in the sound field are the same.  Diffuse fields usually pertain to indoor environments

Reverberant Field

Essentially the same as the diffuse field.  For indoor sound field discussions it is used to contrast direct fields.

NOISE REDUCTION OBTAINED FROM USE OF NOISE BARRIER

If a sound source is in a room with a large amount of

absorption present, blocking the direct path with a

partial barrier may provide adequate noise control.

Indeed, this technique is more often used outdoors,

since even a modest amount of reverberation will

destroy the effectiveness of a shield.

OSHA DECIBEL LEVELS – HEARING PROTECTION

Employee exposure to excessive noise depends several factors including; The loudness of the noise as measured in

decibels (dB) The duration of each employee’s exposure to

the noise Whether employees move between work areas

with different noise levels (decibel levels) Whether noise is generated from one or

multiple sources Generally, the louder the noise, the shorter

the exposure time before hearing protection is required.

PERMISSIBLE NOISE EXPOSURES

Duration per day, in hours

Sound level in dB* - Decibel

level8 906 924 953 972 100

1.5 1021 105

0.5 1100.25 or less 115

DECIBEL LEVELS OF ENVIRONMENTAL SOUNDS

Source--Dangerous Level dBA SPL

Produces Pain (120-140dB)

Jet Aircraft During Takeoff (at 20 meters) (130dB)

SnowmobileTractor Without Cab (120dB)

Rock Concert (110dB)

Die Forging HammerGas Weed-WhackerChain SawPneumatic Drill (100-105dB)

Home Lawn Mowers (95 to

100dB) Semi-trailers (at

20 meters) (90dB)

Source--dBA SPL Discomfort Level

Above (80dB) Heavy Traffic

(80dB) Automobile (at 20

meters) (70dB) Vacuum Cleaner

(65dB) Conversational

Speech (at 1 meter) (60dB)

Quiet Business Office (50dB)

Residential Area at Night (40dB)

Whisper, Rustle of Leaves (20dB)

Rustle of Leaves (10dB)

Threshold of Audibility (0dB)

TYPES OF HEARING PROTECTION

Some types of hearing protection include:

Single-use earplugs are made of waxed cotton, foam, silicone

rubber or fiberglass wool. They are self-forming and, when properly

inserted, they work as well as most molded earplugs.

Pre-formed or molded earplugs must be individually fitted by

professional and can be disposable or reusable. Reusable plugs

should be cleaned after each use.

Earmuffs require a perfect seal around the ear. Glasses, facial hair,

long hair or facial movements such as chewing may reduce the

protective value of earmuffs.

REFERENCES

Health, N. I. (2014, August 08). Center for Disease Control and Prevention. Retrieved from USA.gov:

http://www.cdc.gov/niosh/topics/noisecontrol/

Industrial Noise Control Manual, Revised Edition, National Institute of Occupational Safety and Health (USA)